1. Field of the Invention
The invention relates to a power semiconductor device having a semiconductor body whose electrodes are provided with electrode connections. At least one of the electrodes is formed of several superposed metallization layers and is provided to make a pressure contact connection.
2. Description of the Prior Art
Such a power semiconductor device is described in, e.g. German Pat. Publication DE-OS No. 21 22 487. At least one of the electrodes shown therein consists of an aluminum layer which is in contact with the semiconductor body. The aluminum layer is provided with a silver layer upon its upper surface which, under pressure, presses against a contact electrode that acts as an electrode connection. The silver layer protects the aluminum layer against oxidation and provides a good contact to the contact electrode.
When such power semiconductor devices are provided with electrode connections making pressure contact, which may consist of, e.g., nickel-plated copper contact pieces, and are subjected to drastic load reversals, it frequently causes the device to fail. The chain of events is as follows: The nickel-plated copper contact piece becomes welded together, by its outer edge, with the electrode of the semiconductor body, which, after further changes in the load, leads to cracks in the silicon and thus to a loss of its ability to act as a barrier, and to the burning out of the components. The greater the temperature fluctuations and the contact pressure, the more frequent will be the occurrence of such a failure.
It is an object of the present invention to provide a power semiconductor device with an electrode for making pressure contact that will prevent a welding together of the electrode connection and electrode, and, in addition, provide good lateral conductivity.